The invention is drawn generally to the field of the manufacture of phenol. Specifically, the invention is drawn to a method for the recovery of phenol from an aqueous stream, wherein the phenol is partitioned from the aqueous stream in such a way as to minimize the water and salt content of the phenol.
It is very common in the manufacture of phenol to generate aqueous streams containing significant amounts of phenol either as the free phenol or as a phenate salt. In order to maximize yield and minimize the environmental impact of waste water streams, manufacturers undertake to recover as much of this phenol as possible. The recovered phenol is generally placed back into the process stream for further refining. Phenol containing aqueous streams are generated from a number of sources in a phenol manufacturing facility. A primary source of these streams is from the recovery of phenol from non-phenol organic streams such as cumene and alpha-methylstyrene. The phenol is removed from these organic streams by extraction with an aqueous base such as sodium hydroxide to form an aqueous phenate solution. The phenol is subsequently sprung from the aqueous solution by neutralization with an appropriate acid. The sprung phenol is then separated from the aqueous layer and recycled to crude phenol processing.
A drawback of adding phenol recovered in this fashion to a process stream is that the recovered phenol generally contains a substantial amount of water and dissolved salts carried over from the aqueous streams. The salts may subsequently precipitate in process equipment, causing damage and lengthy shutdowns for cleaning and repairs.
It would therefore be desirable to provide a method for recovering phenol from salt containing aqueous streams that minimizes the quantity of water and dissolved salts carried over into the recovered phenol.
The present invention provides a method for minimizing the content of salt in phenol recovered from salt containing aqueous streams. The method of the present invention makes use of relatively non-polar solvents to improve the separation between phenol and salt containing water solutions. Preferred non-polar solvents are organic streams comprising cumene, alpha-methylstyrene or mixtures thereof due to their ready availability in a phenol manufacturing environment.
By adding a relatively non-polar solvent to a water/phenol mixture prior to separation, the affinity of water for the phenol containing organic layer is reduced. By reducing the affinity of water for the organic layer, the quantity of salt carried into the organic layer is minimized. Further, addition of a relatively non-polar solvent reduces the affinity of phenol for the aqueous phase. Thus the method according to the current invention provides a phenol stream with a substantially reduced salt content. Since any non-polar solvent added to affect the separation must be removed in further processing, care must be taken to minimize the quantity of non-polar solvent added to minimize the further costs of processing the recovered material.
In the process according to the current invention phenol with a low salt content is recovered from a salt containing aqueous stream. The low salt content in the recovered phenol is accomplished by addition of a relatively non-polar solvent to the phenol containing aqueous stream prior to separation. By relatively non-polar as referred to herein is meant non-polar relative to phenol and water.
The process according to the current invention is applicable to process streams comprising water and phenol. In the preferred embodiment, an aqueous process stream is generated by extraction of phenol from an organic stream with an aqueous base such as sodium hydroxide to form an aqueous phenate solution. The phenol is subsequently sprung from the phenate solution by neutralization with an appropriate acid. Prior to separation of the sprung phenol from the aqueous phase, a relatively non-polar solvent is added to the phenol water mixture. The combined mixture is then agitated to effect mixing of the phenol and non-polar solvent. The combined mixture is then separated into a phenol containing organic layer and a waste aqueous layer. Preferred solvents are organic streams comprising cumene, alpha-methylstyrene or mixtures thereof due to their ready availability in a phenol manufacturing plant. The organic streams utilized will generally comprise crude streams of cumene, alpha-methylstyrene or mixtures thereof that have been previously isolated from the decomposition of cumene hydroperoxide in the production of phenol. These streams will therefore very often contain minor amounts of other components. The exact composition of these streams is not critical to the functioning of the method according to the current invention. Rather, it is only important that the solvent composition used be as a whole non-polar relative to water and phenol. Preferably, the relatively non-polar solvent is added in a ratio to phenol of about 0.4:1 to about 1.2:1. More preferably the ratio of non-polar solvent to phenol is about 0.5:1 to about 1:1.